I've used WIFI 'DS-to-DS' & that works (I visited the other town just fine without it crashing)
or do you mean 'Nintendo WFC' - 'cos I've tried that & connected to my 'Nintendo USB WIFI adaptor' & that didn't crash either when the gates opened (didn't have any visitors though)

How about a bit more info
- Which version of AC:WW are you using ?? (U) or (E)
- Are you using a DSLite/DSPhat or DSi ??
- Have you tried turning off 'DS download play'/'Soft-Reset' &/Or Cheat Code Usage' ??

Ha Ha... Actually I meant 'kaisaj' should give more details - but I guess you're having same problem

Well I'm using AC:WW (E) on Dsi with 1.6RC2 & as I mentioned - the WIFI works fine

Unless it's because of yours being (U) or the DXL does Wifi 'differently' - I don't know, but since Normmatt knows there is a problem like this on ACWW and working on it - I guess you'll have to wait a little longer